In general, a truck not only has a larger weight or size than a car, but also has a larger height than a car. Thus, when a car collides with the rear end of a truck, the car may slide under the cargo box of the truck, thereby causing a fatal accident. Therefore, as illustrated in FIGS. 1 and 2, a heavy goods vehicle such as a truck is required to have a rear guard 1 installed at the rear thereof.
The rear guard 1 serves to prevent a small vehicle from sliding under a truck, when the small vehicle collides with the rear end of the truck. As illustrated in FIG. 3, the rear guard 1 is fixed to a guard stay 2. Typically, the guard stay 2 has a bracket structure formed by pressing a steel plate. The guard stay 2 is attached to a rear chassis frame 3 of a truck. Furthermore, the rear guard 1 is made of a rectangular or circular steel pipe, and attached to one ends of both guard stays 2.
In a general car, the front bumper is installed between 250±50 mm and 450±50 mm from the ground. At this time, 250±50 mm indicates a height from the ground to the bottom of the bumper, and 450±50 mm indicates a height from the ground surface to the top of the bumper. Moreover, the rear bumper is installed between 300±50 mm and 500±50 mm from the ground. At this time, 300±50 mm indicates a height from the ground to the bottom of the bumper, and 500±50 mm indicates a height from the ground surface to the top of the bumper. Therefore, although a car collides with another car, the car in the rear does hardly slide under the car in the front. In the case of a truck, however, the rear guard 1 is installed between 550 mm and 650 mm from the ground. At this time, 550 mm indicates a height from the ground to the bottom of the rear guard 1, and 650 mm indicates a height from the ground to the top of the rear guard 1. Therefore, when a car rear-end collides with the truck in front, the car may slide under the truck, thereby causing a fatal accident.
In order to solve such a problem, a structure may be considered, in which the rear guard 1 of the truck is installed at the bumper level of a car. In this case, as illustrated in FIG. 1, a truck having a short distance from a rear wheel to the rear end of the cargo box has no trouble in moving up or down a steep access road, because an angle θ1 between the ground and a line connecting the rear wheel of the truck to the bottom of the rear guard is large. As illustrated in FIG. 2, however, a truck having a long distance from a rear wheel to the rear end of the cargo box has a structure in which the cargo box protrudes to the rear further than that of the truck of FIG. 1. Thus, such a truck has a small angle θ2 between the ground and a line connecting the rear wheel to the bottom of the rear guard. Therefore, when the truck moves up or down a steep access road, the rear guard 1 may be damaged while coming in contact with the ground. Accordingly, in the truck of which the cargo box significantly protrudes to the rear, the rear guard 1 cannot be installed at a low height.
In other words, the truck having a long distance from the rear wheel to the rear end of the car box has a problem in that the rear guard cannot be installed at a low height from the ground because the rear guard is damaged by contact with the ground when the truck moves up or down a steep access road. Besides, when the rear guard is not installed at a position which is sufficiently close to the ground due to the constraint condition of the truck, a car in the rear may slide under the truck in the case where the car collides with the rear end of the truck. In this case, the rear guard may not play its role.